Properties of superconducting Nb/Al/Nb/Al-AlOx-Al-AlOx-Al/Nb/Al/Nb tunnel junctions

Modified geometry (MG) devices, Nb/Al/Nb/Al-AlOx-Al'-AlOx-Al/Nb/Al/Nb, have been fabricated and investigated in comparison with the basic geometry (BG) double-barrier Nb/Al-AlOx-Al'-AlOx-Al/Nb devices. The enhancement of the critical temperature in the Al` film is found to be weaker for the MG devices as compared with the BG devices at temperatures near T=4.2 K but stronger at low T. Indication of an enhancement of dc Josephson critical current density, j(c), at bias voltage V not equal 0 as compared with j(c)(V=O) has been observed in the MG devices for the first time.